Leishmania braziliensis infection can lead to the inflammatory clinical forms of disease, cutaneous (CL) and mucosal leishmaniasis (ML). Peripheral blood mononuclear cells (PBMC) from these individuals secrete high levels of IFN-gamma and TNF-alpha and low levels of IL-10 in response to soluble Leishmania antigen. Lesions of these patients are composed by mononuclear cells infiltrate and very few parasites are observed. Despite the control of parasite multiplication, the immunopathology persists and attempt to modulate inflammatory in-vitro using recombinant IL-10 or monoclonal antibodies anti- IL-12 and anti-IL-15 failed to down-regulate IFN-gamma production in PBMC from these patients, suggesting that another mechanism of regulation of immune response might contribute to pathogenesis of CL and ML. A role of Notch signaling in lymphocyte differentiation, proliferation and cytokine production has been reported. Expression of the Notch ligand, Delta4 in dendritic cells (DCs) was shown to orchestrate differentiation of Th1 cells and, recently, it has been shown that toll like receptor ligand-induced DC and monocytes activation is also dependent upon Notch signaling. Our preliminary data shows that disruption of Notch signaling using gamma secretase inhibitor can decrease Leishmania antigen- induced IFN-gamma production in patients with CL. Also, our data shows that differentiation of human monocytes into CD16+ (pro-inflammatory monocytes) is dependent on gamma secretase activity. In the present proposal we seek to identify the molecules that participate in the Notch signaling (Delta and Jagged) that are involved in the generation and maintenance of inflammatory responses in CL and ML individuals. The patients and controls will be recruited from the L. braziliensis transmission endemic area of Corte de Pedra, Northeastern Brazil. In this endemic area an average of 1000 CL cases and 40 ML cases occurs per year, and our group has been performing clinical and immunological studies in this site for almost three decades. In the endemic are of Corte de Pedra we also found that 15% of the population has positive skin test for Leishmania antigen without symptoms or history of disease. These individuals are known to have sub-clinical L. braziliensis infection and, together with uninfected individuals, will compose the controls we will recruit for our studies. After the conclusion of these studies we should have identified the molecules from Notch signaling that contributes from inflammatory response in CL and ML.